Timing circuit



Dec. 4, 1956 L. E. SHAW 2,773,221

TIMING cmcun Filed Aug. 12. 1952 26 w TO WELDER Q PRIMARY CKT.

INVENTOR Lloyd E. Show .BYZZWMWZ? ATTORNEY United States Patent TllVIING CIRCUIT Lloyd E. Shaw, Newburyport, Mass., assignor to Columbia Broadcasting System, Inc., a corporation of New York, doing business as Hytron Radio & Electronics (10., Salem, Mass., a division of Columbia Broadcasting System, Inc.

Application August 12, 1952, Serial No. 303,986

4 Claims. (Cl. 317-135) This invention relates in general to timing circuits and in particular to a circuit for timing the operation of a welder.

The quality of welds in general is largely determined by the length of time the welding current passes through the objects being welded. This fact leads to the requirement for accurate timing devices with all welders, but particularly with spot welders of the type used generally in the manufacture of electron tubes. Here, for both structural and electrical reasons, welds must be of the highest quality. When the size of the leads commonly used in electron tubes is considered, the timing accuracy of welds becomes of paramount importance. Also, the manufacture of electron tubes is a high-speed production process leading to the further requirement of almost instantaneous resetting of the timer for the next use. Finally, provision must be made for adjustment of the timer if the device is to be of general value, and the repeatability of timing, no matter what the adjustment, is highly important.

Much work has been done in this area and the timing devices are numerous. One timer which has been used utilizes the filament of a lamp to determine the time of welding, the change of resistance of the filament as it is heated being the factor determining the duration of the passage of welding currents. The disadvantages of this system lie in the facts that it is not readily adaptable to work with difierent line voltages, and, more important, timing is not repeatable because of residual heat in the lamp filament.

Another timer which has been used contains small Thyratrons for controlling the welding current. Timers of this type are open to the objections that a warm-up time is needed, additional relays to handle the actual Welding currents are required, and the Thyratrons themselves change with age, destroying timing accuracy.

Elaborate and expensive devices have also been used. These include heavy duty Thyratrons and lgnitrons for interrupting the welding currents. These units for the most part do a satisfactory timing job, but their cost is prohibitive when the many welders used in tube fabrication are each equipped with such a device.

Hence, it is an object of this invention to provide an accurate timing device for welders.

it is a further object to provide a timer composed of inexpensive components.

It is a still further object to provide a timer having short recycling time.

It is another object to provide a simple, rugged, easily adjustable timer for welders.

It is still another object to provide a timer providing positive opening and positive closing of the circuit without the potential variables of relay armature mass, friction, residual magnetism, or spring pressure.

In general, the timer consists in a circuit which includes a relay for closing and a relay for opening the primary of a welder circuit. The relays are D. C. operated to avoid the eltects of transients found in A. C. relay operation.

Patented Dec. 4, 1956 One relay responds to the voltage on a first charged condenser to close the circuit and the second relay responds to voltage on a second condenser which is charged at an adjustable rate to a point at which the second relay opens the circuit. For a better understanding of the invention, together with other and further objects, features, and advantages, reference should be made to the following description which is to be read in connection with the accompanying drawing the single figure of which is a circuit diagram of the welding timer of the invention.

Referring now to the drawing, there are shown A. C. input terminals 12 and 13. Connected in a first loop with terminals 12 and 13 are a switch 14, a resistance 15, a rectifier 16 and a condenser 17. A second loop includes a resistance 18, a rheostat 19 and the coils of a first normally closed relay 20 and second normally open relay 21. A condenser 22 shunts the coil of relay 20. Connected from the junction of the tap of rheostat 19, condenser 22 and the coil of relay 20 is a lead which runs to a resistance 23, then to a fixed contact of double-throw switch 24, which is normally connected to the movable contact of that switch. The other fixed contact of switch 24 is returned to the junction of terminal 13 and condenser 17. The movable contact of switch 24 is con nected to the junction of the coils of relays 20 and 21 and condenser 22. Leads 25 and 26 which terminate at the fixed contacts of relays 20 and 21 respectively form a portion of the input line of the welder primary circuit. The movable contacts of relays 20 and 21 are connected together.

In operation, the unit is originally made ready by closing switch 14. This causes condenser 17 to assume a charge through resistance 15 and rectifier 16. To initiate the timing operation, switch 24 is thrown to the left, as seen in the drawing, which places condenser 17 in series with relay 21 alone, and also in series with relay 20, rheostat 19 and resistance 18. In the case of relay 21, the high current passing through its coil at the instant switch 24 is thrown causes the relay to close immediately completing the circuit between leads 25 and 26 thus energizing the welder primary circuit.

The current through the coil of relay 20 builds up more slowly because of resistor 18 and rheostat 19 in series therewith limiting current flow. Condenser 22, since it is in shunt with the coil of relay 20, gradually becomes charged through rheostat 19 and resistor 18. When the voltage across condenser 22 reaches the tripping voltage of relay 20, contact is broken with lead 25 and the welder primary circuit is opened.

Switch 24 is then released and drops back to its normal position closing the circuit between its movable contact and the fixed contact connected to resistance 23. Condenser 22 then discharges through resistance 23 causing relays 21 and 26 to drop back quickly to their original positions in that order.

As may be seen, the circuit is composed entirely of inexpensive components. The resetting time is very short, being dependent primarily on the value of resistor 23 through which condenser 22 discharges at the release of switch 24. No tubes subject to change or failure with age are required, and no preheating or warm-up time is necessary. The double relay system utilizing direct currents assures positive opening and closing of the control circuit without concern for the transients associated with alternating current relay operation. The particular double relay system used in the invention has the further advantage that both circuit opening and circuit closing are etfected by powered actuation of relays, there being no dependence upon relay drop-out.

While what has been disclosed constitutes a preferred embodiment of the invention, numerous modifications are possible to those skilled in the art without departure from the concepts of the invention. The basic timer can easily be adapted for use in other apparatus and if momentarycontact type operation is "required the control switch could be replaced by a relay having a second set of contacts for locking in the first set of contacts. The foregoing modifications are cited merely as a few examples of those possible. The invention should be limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A timer for opening and closing a circuit comprising, a first normally closed relay and a second normally open relay having their contacts in series relationship in said circuit, a first capacitor in parallel with said first relay, a second capacitor, means for charging said second capacitor, means for applying the charge from said second capacitor directly tothe winding of said second relay, and to the parallel combination of said first relay winding and said first capacitor, whereby said circuit is closed substantially immediately and reopened upon the charging of said first capacitor to a voltage equal to the tripping voltage of said first relay.

2. A timer for opening and closing a circuit comprising, a first normally closed relay and a second normally open relay having their contacts in series relationship in said circuit, a double-throw switch, a capacitor and a rheostat connected in series through one side of said double-throw switch, means for applying a direct voltage through said one side of said double-throw switch to the winding of second relay alone and to the combination of said rheostat and said capacitor, whereby said second relay closes said circuit substantially instantaneously and said first relay opens said circuit upon the charge on said capacitor exceeding the tripping voltage of said first relay, and a resistor connected across said capacitor through the other side of said switch for discharging said capacitor to reset said first and second relays to their normal positions.

3. A timer for opening and closing a circuit comprising, a source of alternating voltage, a single-throw switch, a first resistor, a rectifier, and a first capacitor in series circuit relationship, whereby closing of said switch causes charging of said first capacitor, a first normally open relay, a double-throw switch having one movable and two fixed contacts, one end of the coil of said first relay being connected directly to one side of said first capacitor, the other end of the coil of said first relay being connected to the movable contact of said double-throw switch, one of said two fixed contacts being connected to the other side of said first capacitor, a second normally closed relay, a second capacitor connected in parallel with the coil of said second relay, a second resistor, a rheostat having a movable tap, and a third resistor being connected in series from the junction of said first capacitor and said rectifier 'to the other fixed contact of said double-throw switch,

one junction of said capacitor and the coil of said second relay being connected to the junction of the movable tap of said rheostat and said third resistor, the other junction of said second capacitor and said coil of said second relay being connected to the junction of said other end of the coil of said first relay and said movable contact of said second switch, the movable contacts of said first and second relays being connected together, the :fixed contact of said first relay being connected to one side of said circuit, the fixed contact of said second relay being connected to the other side of said circuit, whereby closing of said second switch in a first direction causes said normally open first relay substantially immediately to close said circuit, said second capacitor slowly assuming a charge until said normally closed relay opens thereby opening said circuit, release of said second switch causing said second capacitor to discharge through said third resistor, said first and second relays resuming their normal positions.

4. A timer for opening and closing a circuit comprising, a source of alternating voltage, a first switch, a rectifier and a storage capacitor in series circuit relationship whereby said first capacitor may be charged relatively quickly by closing said first switch, a first normally open relay, a second normally closed relay, a capacitor in parallel with said second relay, a second switch, a rheostat in series with said second switch, said storage capacitor, said paralleled capacitor and second relay, and said second switch also being in series circuit relationship with said first relay, whereby closing of said second switch causes instantaneous actuation of said first relay from said storage capacitor and delayed actuation of said second relay, providing closed circuit conditions for an adjustable period of time.

References Cited in the file of this patent UNITED STATES PATENTS 1,672,049 Almquist June 5, 1928 2,088,416 Hobart July 27, 1937 2,265,203 Six Dec. 9, 1941 2,412,092 Mayle Dec. 3, 1946 2,473,683 Hines June 21, 1949 2,480,678 Skudre Aug. 30, 1949 2,515,968 Shanklin July 18, 1950 FOREIGN PATENTS 847,227 France June 26., 193.9 715,154 Germany Dec. 15, 1941 

